.relMidBox(200px,160px,50%);

.relMidBox(@boxWidth, @boxHeight, @top: 50%, @left: 50%) {
  .relMidBox {
    position: relative;
    &-bd {
    /*user defined start*/
      border: 1px solid #f00;
      background: #fc0;
    /*user defined end*/
      position: absolute;
      top: @top;
      left: @left;
      width: @boxWidth;
      height: @boxHeight;
      margin: -@boxHeight/2 0 0 -@boxWidth/2;
    }
  }
}

